<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    *{
        margin: 0;
        padding: 0;
    }
    ul{
        list-style: none;
        background: pink;
        line-height: 50px;
        text-align: center;
    }
    li{
        float: left;
        width: 100px;
    }
    li:hover{
        background: lightpink;
    }
    .drop{
        position: relative;
        
    }
    .drop:hover .content{
        display: block;
    }
    .content{
        position: absolute;
        display: none;
        background:lightpink;
        width: 100px;
    }
    .row::after{
        content: "";
        display: table;
        clear: both;
    }
    </style>
</head>
<body>
    <ul class="row">
        <li>html</li>
        <li>css</li>
        <li class="drop">js
            <div class="content">
                <p>vue</p>
                <p>react</p>
            </div>
        </li>
    <ul/>
</body>
</html>